OXFORD, Miss. — The investigation into poisoned letters mailed to President Barack Obama and others has shifted from an Elvis impersonator to his longtime foe, and authorities must now figure out whether an online feud between the two men might have escalated into something more sinister.

Paul Kevin Curtis, 45, was released from a north Mississippi jail Tuesday, and charges against him were dropped, nearly a week after authorities charged him with sending ricin-laced letters to the president, Republican U.S. Sen. Roger Wicker of Mississippi and Sadie Holland, an 80-year-old Lee County (Miss.) Justice Court judge.

Before Curtis left jail, authorities descended on the home of 41-year-old Everett Dutschke in Tupelo, a northeast Mississippi town best known as the birthplace of the King himself. On Wednesday, they searched the site of a martial-arts studio once operated by Dutschke, who hasn’t been arrested or charged.

Curtis, who performs as Elvis and other celebrities, describes a bizarre, years-long feud with the former martial-arts instructor, but Dutschke insists he had nothing to do with the letters.

The letters contained language identical to that found on Curtis’ Facebook page and other websites, making him an early suspect.

Federal authorities have not said what led them to drop the charges against Curtis. His lawyers say they’re not sure what new evidence the FBI has found.

On Wednesday, dozens of investigators were searching at a small retail space where neighboring business owners said Dutschke used to operate a martial-arts studio. Officers at the scene wouldn’t comment on what they were doing.

Dutschke’s attorney, Lori Nail Basham, said he is “cooperating fully” with investigators.

“The authorities state to me that no warrant has been issued for his arrest,” she said Wednesday afternoon.

Investigators in gas masks, gloves and plastic suits emerged from the business carrying five-gallon buckets full of items covered in large plastic bags. Once outside, others started spraying their protective suits with some sort of mist.

Dutschke was seen outside the studio observing the search on Wednesday.

Both men say they have met Wicker, and they each have a connection to Holland.

Holland has declined to comment on the case.

She was presiding judge in a case in which Curtis was accused of assaulting a Tupelo attorney in 2003. Holland sentenced Curtis to six months in the county jail. He served only part of the sentence, according to his brother.

Running as a Republican, Dutschke lost a lopsided election to Holland’s son, Steve Holland, in 2007, and observers say the judge publicly chastised Dutschke at a political rally that year.

After being released from jail Tuesday, Curtis described a long feud between himself and Dutschke, but said he’s not sure exactly what started it.

The two worked together at Curtis’ brother’s insurance office years ago, Curtis said.

For his part, Dutschke, a former martial-arts instructor, said he didn’t even know Curtis that well.

“He almost had my sympathy until I found out that he was trying to blame somebody else,” Dutschke said Monday.

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